1. Field of the Invention
The present invention relates to an ink jet recording head, an ink jet recording apparatus employing such inkjet recording head, and a liquid supply system suitable for use therein.
2. Related Background Art
Among various recording methods in printers or the like, the ink jet recording method for forming a character or an image on a recording medium by discharging ink from a discharge port (nozzle) is widely employed in recent years because it is a non-impact recording method of now noise level capable of high-density and high-speed recording operation.
An ink jet recording apparatus is generally provided with an ink jet recording head, means for driving a carriage supporting such recording head, means for conveying the recording medium, and control means for controlling these components. An apparatus executing the recording operation under such carriage motion is called serial scan type. On the other hand, an apparatus executing the recording operation by the conveying of the recording medium only, without moving the ink jet recording head is called line type. In the ink jet recording apparatus of line type, the ink jet recording head is provided with a plurality of nozzles arranged over the entire with of the recording medium.
The ink jet recording head is provided with energy generating means for generating discharge energy to be given to the ink in the nozzle, in order to discharge therefrom an ink droplet. The energy generating means can be an electromechanical converting element such as a piezo element, an electrothermal converting element such as a heat generating resistor, an eletromagnetic wave-mechanical converting element or an electromagnetic wave-thermal converting element for converting electromagnetic wave such as electric wave or laser light into mechanical vibration or heat. Among these, a method for discharging ink droplet by thermal energy can achieve recording of high resolution because the energy generating means can be arranged at a high density. Particularly an ink jet recording head utilizing an electrothermal converting element as the energy generating means can be made compact more easily than a head utilizing the electromechanical converting element, and provides advantages of easily achieving high-density configuration and low manufacturing cost, utilizing the IC technology and the micro fabrication technology showing remarkable progress and improvement in reliability in the semiconductor area.
In the system of ink supply to the ink jet recording head, there are known so-called integral ink tank system in which an ink tank containing the ink is integrated with the ink jet recording head, so-called separated ink tank system in which the ink tank is separated from the ink jet recording head, so-called tube supply system in which the ink tank and the ink jet recording head are connected by a tube, and so-called pit-in system in which the ink tank and the ink jet recording head are provided separately but the ink jet recording head is moved to the position of the ink tank whenever required and is connected thereto for executing ink supply from the ink tank to the ink jet recording head.
When the capacity of the ink tank is increased in order to reduce the frequency of replacement thereof, the weight thereof increases. This means an increase in the weight of the carriage in the recording apparatus of serial scan type. In consideration of this fact, the ink jet recording apparatus of serial scan type requiring the ink tank of a large capacity for example for outputting a large sized recorded image often employs the tube supply system or the pit-in system. Among these, the tube supply system capable of continuous recording over a long period is often employed since, in the pit-in system, the recording operation has to be interrupted during the ink supply operation.
In the following the ink supply system of an ink jet recording apparatus of tube supply system will be explained with reference to FIG. 25.
The ink supply system shown in FIG. 25 is provided with a main tank 1204 containing ink therein, a supply unit 1205 on which the main tank 1204 is detachably mounted, and a recording head 1201 connected to the supply unit 1205 through a supply tube 1206.
The supply unit 1205 is provided therein with an ink chamber 1205c, which is open to the air by an air communicating port 1205g at the upper portion and is connected at the bottom portion to the supply tube 1206. On the supply unit 1205, there are fixed a hollow ink supply needle 1205a and a hollow air introducing needle 1205b of which lower ends are positioned in the ink chamber 1205c and higher ends protrude from the upper face of the supply unit 1205. The lower end of the ink supply needle 1205a is positioned lower than that of the air introducing needle 1205b. 
The main tank 1204 is provided at the bottom thereof with two connector portions composed for example of rubber stoppers for closing the interior of the main tank 1204, whereby the ink tank singly has a hermetically closed structure. The mounting of the main tank 1204 to the supply unit 1205 is executed in such a manner that the ink supply needle 1205a and the air introducing needle 1205b respectively penetrate the connector portions and enter the interior of the main tank 1204. Since the lower ends of the ink supply needle 1205a and the air introducing needle 1205b are positioned as explained in the foregoing, the ink in the main tank 1204 is supplied to the ink chamber 1205c through the ink supply needle 1205a and the air is introduced into the main tank 1204 through the air introducing needle 1205b so as to compensate the pressure decrease resulting in the main tank 1204. When the ink is supplied into the ink chamber 1205c until the lower end of the air introducing needle 1205a is immersed in the ink, the ink supply from the main tank 1204 to the ink chamber 1205c is terminated.
The recording head 1201 is provided with a sub tank 1201b for containing ink of a predetermined amount, an ink discharge portion 1201g having an array of plural nozzles for ink discharge, and a flow path 1201f connecting the sub tank 1201b and the ink discharge portion 1201g. In the ink discharge portion 1201g, a face having the nozzle apertures is directed downwards, so that the ink is discharged downwards. Each nozzle in the ink discharge portion 1201g is provided with the aforementioned energy generating means. The sub tank 1201b is positioned higher than the ink discharge portion 1201g, and the supply tube 1206 is connected to the sub tank 1201b. Between the sub tank 1201b and the flow path 1201f, there is provided a filter 1201c having a fine mesh structure in order to prevent clogging of the nozzle resulting from the entry of fine foreign particles into the ink discharge portion 1201g. 
The area of the filter 1201c is so selected that the pressure loss in the ink does not exceed a tolerance value. The pressure loss in the filter 1201c increases as the mesh thereof is fiber or the ink flow rate through the filter is higher, but is inversely proportional to the area thereof. Since the pressure loss tends to become higher in the recent recording head of high-speed, multi-nozzle and small recording dots, the area of the filter 1201c is selected as large as possible to suppress the increase in the pressure loss.
Since the nozzle in the ink discharge portion 1201g is open to the air and directed downwards, the interior of the recording head 1201 has to be maintained at a negative pressure relative to the atmospheric pressure in order to prevent ink leakage from the nozzle. On the other hand, an excessively large negative pressure causes entry of gas into the nozzle, whereby the nozzle becomes incapable of discharging ink. Therefore, in order to maintain a suitable negative pressure in the recording head 1201, the recording head 1201 is so positioned that the nozzle aperture face is higher, by a height H, than the ink liquid level in the ink chamber 1205c thereby maintaining the interior of the recording head 1201 at a negative pressure corresponding to the water head H. In this manner the nozzle can be maintained in a state filled with ink and forming a meniscus at the aperture face.
The ink discharge from the nozzle is executed by driving the energy generating means thereby pushing out the ink in the nozzle. After the ink discharge, the nozzle is filled with ink by the capillary force, from the side of the flow path 1201f. During the recording operation, the ink discharge from the nozzle and the ink filling into the nozzle are repeated whereby the ink is sucked from time to time from the ink chamber 1205c through the supply tube 1206.
As the ink in the ink chamber 1205c is sucked into the recording head 1201 and the ink liquid level in the ink chamber 1205c becomes lower than the lower end of the air introducing needle 1205b, air is introduced into the main tank 1204 through the air introducing needle 1205b. Along with this operation the ink in the main tank 1204 is introduced into the ink chamber 1205c whereby the lower end of the air introducing needle 1205b is immersed again in the ink in the ink chamber 1205c. Through the repetition of such operations, the ink in the main tank 1204 is supplied to the recording head 1201 along with the ink discharge therefrom.
In the sub tank 1201b of the recording head 1201, there are gradually accumulated gas entering the plastic material constituting the supply tube 1206 etc. and gas dissolved in the ink. In order to discharge useless gas accumulated in the sub tank 1201b, a gas discharge tube 1211 connected to a gas discharge pump 1211a is connected to the sub tank 1201b. However, in order to maintain the interior of the recording head 1201 at a suitable negative pressure, the discharge tube 1211 is provided with a valve 1211b, which is opened only in a gas discharging operation in such a manner that the pressure inside the recording head 1201 does not exceed the atmospheric pressure.
In order to eliminate viscosified ink clossing the ink discharge portion 1201g or a bubble generated from gas dissolved in the ink therein, the ink jet recording apparatus is usually provided with a recovery unit 1207, which is provided with a cap 1207a for capping the nozzle face of the recording head 1201 and a suction pump 1207c connected to the cap 1207a, and which eliminates the viscosified ink or accumulated bubble from the ink discharge portion 1201g by activating the suction pump 1207c thereby forcedly sucking the ink in the ink discharge portion 1201g. 
In such suction recovery operation, a faster ink flow speed allows to effectively eliminate the viscosified ink and the bubble so that the cross section of the flow path 1201f is made small in order to increase the ink flow speed therein. On the other hand, the cross section of the filter 1201c is made as large as possible as explained in the foregoing, so that the flow path 1201f is made smaller in the cross section at the downstream side of the filter 1201c. 
In the foregoing, there has been explained the conventional ink supply system in case of a tube supply system, but, also in the integral head tank system, separated head tank system or pit-in system, the configuration at the downstream side of the filter of the recording head is basically same as in the above-described tube supply system, and the difference lies only in the configuration of the ink supply path from the ink tank to the recording head.
However, the aforementioned conventional configuration may be unable to completely eliminate the bubbles, thereby eventually result in deterioration of the recording quality such as by discharge failure or ink dripping resulting from the bubbles.
In the following there will be explained drawbacks of the conventional configuration shown in FIG. 25, when bubbles are accumulated in the ink flow path 1201f at the downstream side of the filter 1201c. 
A portion under the filter is reduced in the cross section of the ink flow path and constitutes a portion where the flow becomes stagnant even by the recording operation of the recording head, so that the bubbles tend to remain. Particularly in a recording head designed for multiple nozzles and a higher recording speed, the filter area has to be increased so that the ink stagnant portion increases in the ink flow, whereby the bubbles tend to remain under the filter. Particularly in case the filter and the ink flow path are positioned vertically with respect to the direction of gravity, the bubbles gather by the floating force under the filter. However, a filter portion in contact with the bubbles is incapable of filtering the ink, so that the effective filter area is inevitably decreased.
Also the ink flow path, having a small cross section, is clogged by a large bubble whereby the substantial flow resistance increases to hinder the required ink supply to the nozzle, thus eventually resulting in ink dripping or the like.
Also the bubbles in the ink discharge portion utilizing an electrothermal converting element as the energy generating means include those coming from the upstream side, namely those generated in ink passing through the filter, and those resulting from ink discharge, namely, after ink discharge by bubble generation in the ink, those not dissolved again in the ink at the extinction of the bubble and gradually accumulated in the ink. Such bubble gradually grows and may enter the nozzle or may clog the connecting portion between the nozzle and the ink discharge portion thereby resulting in discharge failure or ink dripping. Particularly in the vicinity of the ink discharge portion, fine bubbles tend to gather because the temperature in the vicinity of the heater rises to render re-dissolution of the bubbles into the ink difficult, whereby the bubble tends to grow to a size causing detrimental effect on the recording.
Furthermore, in the conventional configuration, since the cross section of the ink flow path is reduced, the generated bubbles in the ink flow path can be discharged by the recovery operation of the recording head, but the ink supply to the nozzle is hindered if the bubble grows so fast as to interrupt the flow path. In order to avoid such situation, it is necessary to discharge the bubble by executing the recovery operation frequency, but there results a drawback that the ink is wasted at each recovery operation.
On the other hand, if the cross section of the ink flow path is so increased as xe2x80x9cnot to interrupt the ink flow path by the bubblexe2x80x9d or xe2x80x9cto eliminate a portion where the ink flow tends to become stagnantxe2x80x9d, the bubble becomes easily movable so that, even if the ink is strongly sucked in the suction recovery operation, there is only sucked the ink but the bubble itself merely moves upstream in the ink flow path and cannot be discharged by suction.
Also since the filter has a fine mesh structure, when the bubbles reach and are absorbed under the filter, there is formed a meniscus by the ink in the sub tank, in the space in the mesh of the filter. As a result, the bubbles under the filter cannot pass through the filter to the upstream side but are accumulated under the filter.
A filter portion under which the bubbles are accumulated cannot pass the ink, thereby reducing the effective area of the filter and increasing the ink flow resistance, whereby the ink supply amount from the sub tank to the ink flow path and the ink supply amount from the ink flow path to the ink discharge portion become unbalanced to result in a discharge failure. Also, if the bubble accumulation in the ink supply portion and the deficient ink supply from the sub tank to the ink supply portion further proceed, the ink in the ink discharge portion may result in a fatal drawback such as the ink supply to the nozzle being impossible.
Also in case the small bubbles accumulate under the filter grow to a large bubble, such large bubble moves under the filter by the vibration of the recording head in the printing operation or the like, thereby securing, though unstably, an effective filter area for ink supply from the sub tank to the ink flow path, but, in case the small bubbles accumulated under the filter do not assemble and remain as a gathered group of small bubbles, such small bubbles stick to the filter even under the vibration of the recording head in the printing operation or the like and do not easily move, whereby the effective filter area for ink supply from the sub tank to the ink flow path becomes difficult to secure. Consequently there is encountered a situation where the ink supply to the nozzle cannot be realized.
Also, in order to avoid deterioration in the recording quality such as discharge failure or ink dripping, resulting from such bubbles, it becomes necessary to frequently repeat the recovery operation for removing the bubbles accumulating under the filter.
Such drawback is conspicuous in a recording head having a larger ink supply amount from the sub tank to the ink flow path and tending to show a larger pressure loss in the filter, namely a recording head with multiple nozzles for recording with small dots.
The object of the present invention is to provide an ink jet recording head capable of preventing drawbacks resulting from the bubbles generated at the downstream side of the filter while minimizing the waste of ink, an ink jet recording apparatus utilizing such ink jet recording head, a liquid supply system and a liquid filling method advantageously employable therein.
The above-mentioned object can be attained, according to the present invention, by a liquid supply system which is provided with a liquid supply path to a liquid holding portion holding liquid at the downstream end in the liquid supply direction, and a filter in the liquid supply path and in which the liquid can be supplied from the upstream side of the filter to the downstream side thereof in the vertical direction in the direction of gravity, the system comprising:
a member for dividing a portion of the filter in contact with the downstream side into a gas holding area and a liquid holding area;
wherein the gas held in said gas holding area is in communication with gas present between the downstream side of the filter and the liquid holding portion in the aforementioned downstream end.
In the liquid supply system of the present invention, as the downstream side of the filter secures a gas holding area for holding gas, a bubble eventually generated at the downstream side of the filter, being smaller than the gas held in the gas holding area, is eventually united with such gas. Thus it is rendered possible to avoid that the small bubbles are mixed in the liquid flow path or remain as a gathered group. Also the downstream side of the filter is divided into a gas holding area and a liquid holding area to stably secure an effective filter area, whereby the liquid supply from the upstream side of the filter can be stably executed without deficiency even when the liquid of a large amount is consumed at the downstream end of the liquid supply path.
At the downstream side of the filter, there is preferably formed a liquid connecting structure for holding the liquid, present in the downstream side of the filter, by the surface tension in the gas holding area thereby being connected across the filter with the liquid at the upstream side thereof. In this manner, the liquid smoothly moves between the upstream and downstream sides of the filter through the liquid connecting structure in case of liquid consumption at the downstream end of the liquid supply path or in case of a gas volume change in the gas holding area resulting for example from a change in the environmental temperature.
The liquid connecting structure is preferably provided in the vertical direction and is provided with a groove-shaped structure of which the upper end is in contact with the downstream face of the filter. In such case, the gap t between the groove-shaped structure and the filter is selected in a range 0xe2x89xa6txe2x89xa61.0 mm whereby the liquid held by the groove-shaped structure is in satisfactory contact with the filter. Also in the downstream side of the filter, the liquid supply path may be composed of a cover member constituting a lateral face thereof and a main body member constituting another face and jointed to the cover member, and the groove-shaped structure may be provided at least in the cover member. In such case, the groove-shaped structure in the cover member may be formed as a projection with a slit, protruding from a joint plane of the cover member with the main body member and adapted to hold liquid by the surface tension, whereby, even if the cover member and the main body member are jointed by an adhesive, the slit of the groove-shaped structure for holding liquid can be prevented from entry of the adhesive.
Also the liquid supply path may be so constructed as to have a first liquid chamber at the upstream side of the filter and a second liquid chamber including the aforementioned gas holding area at the downstream side of the filter. In such case, it is possible to form a valve mechanism at the upstream side of the first liquid chamber or to provide the first liquid chamber with an air communicating aperture which can be opened or closed, whereby, in case the gas is accumulated in the second liquid chamber, suction is executed from the side of the second liquid chamber in a state where the valve mechanism or the air communicating aperture is closed, thereby reducing the pressure of the first and second liquid chambers to a predetermined value, and then the valve mechanism or the air communicating aperture is opened to fill the first and second liquid chambers with liquid of respectively appropriate amounts from the upstream side, even when gas is accumulated in the first and second liquid chambers to reduce the liquid amounts therein.
It is also possible to provide the liquid supply path at the downstream side of the filter with two liquid chambers. By the gas inflation or the vapor pressure increase in the second liquid chamber, the liquid therein is pushed out to the downstream end of the liquid supply path or returned to the first liquid chamber through the filter. However, an unexpected pushing out of the liquid in the second liquid chamber to the downstream end of the liquid supply path is undesirable, and the liquid in the second liquid chamber cannot return to the first liquid chamber through the filter since, in the second liquid chamber, the filter is in contact with the gas holding area. Therefore, by forming a third liquid chamber having a liquid holding portion adjacent to the gas in the gas holding area, the liquid held in the third liquid chamber can smoothly flow in the first liquid chamber through a contact portion with the filter even in case of gas inflation or vapor pressure increase in the second liquid chamber, whereby the liquid in the second liquid chamber is not unexpectedly pushed out from the downstream end of the liquid supply path. The contact area of the liquid held in the third liquid chamber with the filter can be maintained constant regardless of the liquid amount held in the third liquid chamber by providing the third liquid chamber with a desired number of liquid holding members. The liquid holding on the liquid holding member can be achieved by utilizing the surface tension of the liquid.
According to the present invention there is also provided an ink jet recording head provided with a first liquid chamber and a second liquid chamber separated by a filter and respectively containing liquid therein, and a liquid discharge portion connected directly with the second liquid chamber and adapted to discharge the liquid supplied from the second liquid chamber, in which the liquid can be supplied from the first liquid chamber to the second liquid chamber through the filter, comprising:
a member for dividing a portion of the filter in contact with the second liquid chamber into a gas holding area and a liquid holding area;
wherein the gas held in the gas holding area is in communication with the gas present in the second liquid chamber.
Also in the ink jet recording head of the present invention, since there are provided the first and second liquid chambers separated by the filter and the member for dividing the portion of the filter in contact with the second liquid chamber into the gas holding area and the liquid holding area in a state capable of liquid supply from the first liquid chamber to the second liquid chamber and the gas held in the gas holding area is in communication with the gas present in the second liquid chamber, it is rendered possible to resolve the drawbacks resulting from the bubbles generated at the downstream side of the filter as in the aforementioned liquid supply system of the present invention, thereby enabling stable ink discharge from the discharge portion.
It is thus rendered possible to prevent deterioration in the recording quality such as discharge failure or so-called ink dripping, resulting from the bubbles, and also to reduce the number of recovery operations for eliminating the bubbles accumulated under the filter.
Also a configuration in which the liquid held in the liquid holding area is in communication with the second liquid chamber whereby the liquids in the first and second liquid chambers can reversibly move enables stable liquid discharge from the discharge portion even when the gas volume in the second liquid chamber repeats inflation and contraction.
According to the present invention, there is also provided an ink jet recording apparatus comprising:
support means for supporting the aforementioned ink jet recording head of the present invention;
suction means for forcedly sucking ink in the ink jet recording head from a liquid discharge portion thereof; and
a valve mechanism for opening or closing of a first liquid chamber of the ink jet recording head to or from the exterior thereof.
In the ink jet recording apparatus of the present invention, being provided with the suction means and the valve mechanism, the suction means is at first activated in a state where the valve mechanism is closed, to reduce the pressure in the ink jet recording head to a predetermined value, and then the valve mechanism is opened to fill the first and second liquid chambers with liquid of respectively appropriate amounts, even when gas is accumulated in the first and second liquid chambers to reduce the liquid amounts therein.
According to the present invention there is also provided a liquid filling method for use in a liquid supply system in which the first and second liquid chambers respectively holding liquid are separated by a filter while the liquid is held at the downstream side of the second liquid chamber in the liquid supply direction from the first liquid chamber to the second liquid chamber and gas is present in the gas holding area for separating the filter and the liquid in the second liquid chamber in a state capable of liquid supply from the upstream side of the filter to the downstream side thereof, the method comprising:
a step of closing the first liquid chamber from the exterior;
a step of executing suction from the downstream side of the second liquid chamber in a state where the first liquid chamber is closed, thereby reducing the pressure of the first and second liquid chambers; and
a step, after the pressure decrease of the first and second liquid chambers, of opening the first liquid chamber to the exterior.
It is thus rendered possible to fill the first and second liquid chambers with liquid of respectively appropriate amounts, even when gas is accumulated in the first and second liquid chambers to reduce the liquid amounts therein.